The invention relates to a gas burner particularly for use in ovens, incinerators etc.
In the periodical Norsk VVS, 5/97 a burner is disclosed with low emissions of polluting exhaust gases. The burner has a cylindrical burner housing at one end of which combustion air may be introduced. Centrally in the burner housing and extending coaxially with the housing, a tubing or lance is arranged, into one end of which a gaseous fuel such as propane is to be introduced. At the other end of the tubing a series of radially extending holes is provided through which the gas can enter and mix with the combustion air. The end of the tubing is closed with a wall. Upstream of the holes, between the tubing and the burner housing, baffle plates are arranged in a radial pattern for tangential deflection of the combustion air so that it will flow in a vortex, i.e., helically within and along the walls of the burner housing, downstream of the baffle plates.
This burner has acceptable performance with respect to NOx content in the exhaust gases and with respect to flame stability. By flame stability is meant the burner""s ability to maintain the flame under varying flow conditions and for variations in the relative proportions of supplied fuel and air. A NOx content as low as 40 ppm can be obtained with propane. The burner is, however, not well suited for the use of natural gas as the fuel source, as this leads to low flame stability and a high content of CO and unburned hydrocarbons in the exhaust gases.
From the periodical Norsk VVS it is also known to conduct a partial pre-mixing of gas and air, wherein the gas is introduced to the air upstream and downstream relative to the baffle plates.
EP patent application No. 672 865 (General Electric Company) discloses a burner for a gas turbine, where gas is introduced radially between baffle plates and a burner head. This burner is adapted for use with gas under high pressure and is not suited for low pressure burners.
U.S. Pat. No. 3,469,790 (Duncan) discloses a burner head with radial baffle plates, wherein gaseous fuel is introduced both between the baffle plates and just upstream of the baffle plates. This solution is characterized by a short mixing time which causes an inhomogeneous mixture and high emissions of NOx. The concept of this patent is primarily developed for adaption of the flame to different burner housings and not for low emission of pollution.
The main object of the invention is the provision of a one-step burner with partial pre-mixing and premixing which enables the use of relatively light fuel gases with no performance reduction and with acceptable stability. Heavy gases in the context of this specification would be, e.g. propane, butane and mixtures of these (LPG), whereas light gases include, e.g. natural gas with the naturally occurring variations (LNG, CNG). xe2x80x9cSpecial gasesxe2x80x9d would be, e.g. hydrogen, carbon monoxide and mixtures of these, as well as low value gases.
It is a further object to provide a burner which gives lower emissions of NOx and CO compared to previously known burners. This is to be obtained in combination with a high flame stability and a high level of available adjustment possibilities.
With the burner according to the present invention, good flame stability and low emissions of pollution can be achieved with seemingly unfavorable mixtures of fuel and air. This is achieved utilizing:
a partially pre-mixed fuel/air mixture flowing along the gas tube, which creates a fuel rich shear layer,
a hot backwards and centrally flowing exhaust gas continuously igniting the above mentioned gas mixture and thereby ensuring good stability, and
a main flow of mixed air and fuel which becomes ignited and burns at a low temperature outside the conical end of the flame tubing.